1. Field of the Invention
The present invention relates generally to thermal barrier coatings, and more particularly to thermal barrier coatings of ceramics impregnated with a glass and methods of preparing same.
2. Description of the Related Art
Thermal barrier coatings are used in a wide variety of high temperature applications. For example, a thermal barrier coating of yttria-stabilized zirconia, such as ZrO.sub.2 (8wt.%)Y.sub.2 O.sub.3, may be used to protect critical components in thermal engines.
Typically, a bond coat is initially plasma sprayed upon the component to be protected (hereinafter referred to as the "substrate"). The bond coat may be, for example, a superalloy such as Ni-Cr-Al-Y or Co-Cr-Al-Y. Subsequently, the yttria-stabilized zirconia coating is plasma arc sprayed upon the bond coat.
Thermal barrier coatings, such as the above-mentioned yttria-stabilized zirconia coating, increase the capabilities of the substrate material because they are thermally insulating and strain-tolerant. Therefore, increased engine efficiency, durability and power may be achieved.
In practice, thermal barrier coatings have only met with limited success because they tend to degrade and fail at elevated temperatures. Analysis has shown that this degradation and failure is most often caused by oxidation of the bond coat and thermal fatigue of the yttria-stabilized zirconia coating. Plasma sprayed ceramic coatings contain cracks, which result from solidification of sprayed particles, and up to 10% porosity by volume. Though these defects are helpful in reducing the affects of thermal stresses, they also promote oxidation by facilitating penetration of oxygen and other corrosive compounds through the yttria-stabilized zirconia coating to the bond coat. Consequently, conventional thermal barrier coatings have met with only limited success.